1. Field of the Invention
The present invention relates to a digital watermarking technology, and it particularly relates to an apparatus and method for embedding a digital watermark and an apparatus and method for extracting a digital watermark.
2. Description of the Related Art
The number of Internet users has rapidly increased in recent years and we are now entering the age of the broadband, or a new stage in the utilization of the Internet. Since communication bandwidth has greatly expanded in broadband communication, the distribution of items containing large bodies of data such as audio, still image, and video can be enjoyed with ease. When the distribution of such digital items becomes popular, a highly efficient method of protecting the copyright of their contents will be required.
In the present situation, the copyright is not protected well so that users can easily copy such contents distributed via the Internet. Therefore, technology for embedding information on the originator of the content and the user into the content as a digital watermark has been developed. By using this watermarking technology, it becomes possible to extract the digital watermark from the content distributed via the network, and thereby detect an illegal use and track the distribution route of an illegal copy.
In the reference [1], the applicant has proposed a digital watermarking technology which can detect a location in which a given watermark is to be stickily embedded and can improve the robustness of the watermark embedded in the location.
A digital watermark is embedded in the content data in a way that the watermark is perceptually invisible to users in order to prevent malicious attacks. However, the content data will be subject to various operations during the distribution and utilization, for instance, signal processing such as compression, various types of filtering, modification by users, or attacks on the watermark information. In such processes, a part of the digital watermark may be possibly altered or removed. Therefore the digital watermark should be robust enough to withstand such operations.
In the digital watermark extraction method of the reference [1], there are a plurality of candidate locations in which a digital watermark is to have been embedded. A correct watermark position is determined using an anticipated watermark and the anticipated watermark is detected at the determined watermark position. This watermark extraction method needs to be improved so as to be applied for a case in which there is no available anticipated watermark. Moreover, there is a room for further improvement on a computational cost for evaluating robustness of a digital watermark at the embedding side.
Related Art List:
[1] JP 2003-244419 A